Telephone system



April 28; 1931.. A. w. STEINKE 1,802,449

TELEPHONE SYSTEM Original Filed Aug. 21, 1926 Inventor mm m. 51mm Hit-H;

Patented Apr. 28, 1931 PATENT OFFICE AUGUST W. STEINKE, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO AlVLERIGAN ELECTRIC COMPENY, INQ, OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE Application file-i August 21, 1926, Serial No. 130,536. Renewed August 22, 1930.

The present invention relates, broadly stated, to telephone systems.

More particularly, the invention is concerned with a novel cord circuit for telephone systems in which common battery lines terminate in jacks at operators switchboards.

It is the general aim of the invention to provide a cord circuit which warrants maximum efiiciency, and requires a minimum eifort on the part of the operator. Accordingly, all operations, such as listening in, i. e., answering a call by connecting the operators head set to the cord circuit, and ringing the called party, etc., are made automatic. This, of

course, necessitates a departure from the usual, since one function depends to a certain degree on other functions; therefore, calling, ringing, and disconnect supervision have also been considered in designing the present cord circuit, and they also show novel features, not found in prior systems.

In accordance with the foregoing, one object of the invention is to prevent two operators from answering a call simultaneously. This is accomplished by provisions cooperating with the sleeve relay in the answering end of the cord, which prevent sleeve relays of other cords from energizing, after-the sleeve relay of one cord has once been operated. Since the energization of the sleeve relay conditions the functions of the cord, e. g., adapts the cord to be used for extending a call, only one cord will be so conditioned. If a plurality of operators notice the call signal of a line, and attempt to answer the call simultaneously, only one cord will, therefore, be adapted to be used for executing the call. This provision consists ofa resistance normally connected in series with the sleeve relay. Upon energizing, the sleeve relay shunts out this resistance, and incapacitates sleeve relays of other cords to operate.

Since only one out of a plurality of cords is conditioned for answering a call, the operator handling this cord must receive a conspicuous signal, which indicates to her that she has to answer. Accordingly, another object of the invention resides in the provision of a flashing listening indication. The operator who receives this indication answers the call, and other operators, if there were any who tried to answer the call, Withdraw the plugs.

In accordance with the general aim of the invention, e. g., to design an efficient cord circuit, there are means provided which permit an operator to handle a plurality of cords simultaneously or rather to say, in quick succession, without mutual interference. The phraseology of the art terms this, advance plugging in. It is meant thereby that an operator can, for example, connect two or more cords to calling lines, and answer later, if the traiiic makes this desirable.

Now, because her head set is common to all the cords an operator handles, means are provided in the present invention, to prevent the connection of the head set to more than one plugged cord circuit at a time. This means represents another object of the invention,

and consist in provisions cooperating with the relay which automatically connects the head set to the cord in use, which relay prevents similar relays in other cords from operating. In other words, only one cord can establish connection with the head set, other cords are prevented from doing so.

A further object is to register all extensions completed at a switch-board, regardless whether the called parties answer or not. In accordance with this object, a meter registers 'when the operator inserts a calling plug into the jack of a called line.

A further object is to ring a called line automatically. The operator merely initiates ringing by depressing the proper frequency key for operating the called partys bell. Withthis action, the operator has completed her part in the establishment of a connection.

The calling party has ringing control, e. g., if the called subscriber does not answer, the calling party, replacing his receiver, automatically disconnects the ringing equipment from the cord circuit. This provision represents a further object of the invention.

Still another object resides in means to transmit to the calling subscriber a ring-backtone while the called subscriber is being rung, which tone is of a constant frequency, re-

gardless of the frequency selected for ringing the called line.

There are other objects and features which will be apparent from the detailed description which is yet to follow, and which should be read in connection with the accompanying drawing forming a part of this specification.

At the left of the drawing there is shown the central ofiice equipment of a line A, comprising the line conductors T and R, which terminate in a jack J which is connected in multiple with other jacks appearing in other operators positions, jack J representing the multipled connection of jack J in a second operators position. L signifies the line signal, 1 is the line relay and 2 indicate the cutoif relay.

At the right of the drawing, there is shown the central oiiice equipment of a line B, all parts being identical to the parts enumerated in connection with line A.

The subscribers substation equipment is omitted in order to simplify the drawing. Either of the lines may serve a plurality of substations, e. g., may be a party line, or it may be an individual line. The invention is not specifically concerned with the substation apparatus; any well known equipment may be used.

At C is shown the novel cord circuit, comprising the answering plug P and the calling plug P, as well as a number of relays and signaling apparatus whose functions will be described in due course.

0 signifies a well known operators head set. This head set is common to a number of cords, similar to the one illustrated at C, and is accessible to the cords by way of the common conductors 80, 81 and 82.

At I is shown an interrupter equipment comprising the relays 15 and 16. This equipment is common to a plurality of cords circuits, such as C, and accessible to the cords over the common conductor 23. The lamp 19 is a pilot lamp, i. e., it is common to a position, whereas the lamps 22 and76 are individual to a cord circuit. The purpose of the interrupter equipment is to furnish interrupted current for the supervisory lamps, to flash the lamps in. accordance with the invention, as intimated previously. 7

M indicates the meter equipment comprising the metering relay 37, the meter magnet- 39, and the meter mechanism 17. This equipment is also common to a plurality of cords and is accessible over the conductor 24;.

There is a common resistance coil shown at 46, accessible to the cords by way of conducgardless of the frequency projected out on the called line for ringing the bells of a called substation, as has been explained elsewhere.

FG shows a number of conductors 6265, inclusive, leading to ringing current generators of various frequencies, such as 16, 33, 50, and 66 cycles, respectively; these frequencies being most commonly used in telephone exchanges; there are also shown the frequency selecting keys 93, inclusive, for connecting the cord with a certain frequency; and the starting keys 66-69, inclusive, for starting the ringing. These latter keys operate simultaneously with their corresponding frequency selecting keys, but their operation is a momentary one, whereas the fre quency selecting keys are self-locking and remain closed. The'ringing current source is common to a number of cords and accessible to them over the conductors 62 to 65 in- 'clusive.

Throughout the drawing, there are shown a number of battery and ground connections. It will be understood, however, that this is done merely for convenience of description in accordance with a common practice, and that only one battery is employed in actual installations, preferably with the plus pole grounded.

Having given a general description of the invention and a brief explanation of the drawing and the symbols used, a detailed account of its operation will now be presented. For this purpose it will be assumed that a subscriber at substation A has taken off the receiver from the switch-hook in order to extend a call to the subscriber B.

The line relay 1 operates in response to the subscriber at A removing the receiver from the switch-hook and closes an obvious circuit for the line signal lamps L, L and other similar lamps in other operators positions in which this line is multipled. The circuit for the line relay 1 extends from battery, winding of relay 1, armature 4 and its back contact, line conductor R, subscribers substation, line conductor T, armature 5 and its back contact to ground. The operators, noticing the lighted line lamps L, L and other similar lamps associated with that line, will insert their calling plugs in jack associated with that line appearing in their position. It will be assumed that the operator in whose position cord circuit C appears is the first operator to notice the lighted line lamp in her position, lamp L, and is the first operator to insert her calling plug P in the corresponding jack J. A circuit is now completed from ground through winding of the cut-cif relay 2, sleeve of jack J, sleeve of plug P, resistance 14, winding of the sleeve relay 10, to battery. The cut-off relay 2 and the sleeve relay 1O operate over this circuit. Relay 2 operates its armatures 4' and 5 and removes thereby the line relay 1, which deenergizes and extinguishes the line signal lamps L, L etc. The calling line is new connected through to the cord circuit over the tip and ring contacts of the jack and plug, and the following circuit for the energization of the supervisory relay is closed: ground, upper winding of the supervisory relay 20, talking conductor 6 of the cord circuit, tip of plug and jack, line conductor R, calling substation, line conductor T, ring of jack and plug, talking conductor 7 of the cord circuit, andlower winding of the supervisory relay 20 to battery.

The operation of the sleeve relay 10 will first be discussed in detail. Relay 10 closes armature 13 and thereby shunts out the resistance 14. This resistance 14 is normally connected in series with the winding of sleeve relay 10. In case number of operators attempt to answer the call, only one of the sleeve relays of the various cords will operate, that associated with the cord circuit of the operator first to inspect her plug. Upon energizing in a manner that has been eX- plained, the sleeve relay shunts out the re sistance 14, thereby shunting the sleeve relays of other cords and preventing them from operating. Therefore, only one cord can establish connections with a calling line. The operator who is supposed to answer the call, that is, the operator in whose cord circuit the sleeve relay 10 has energized, receives now a conspicuous signal that she has to answer the call. This is done in the following manner. 7

As has been explained, the sleeve relay 10 and the supervisory relay 20 are operated. A circuit is therefore established from ground, armature 11 and its front, contact, armature 21 and its front contact, armature 12 and its front contact, armature 42 and its back contact, resistance 33, winding of relay 30, common conductor 45, and common resistance 46 to ground. The relay 30 will operate in this circuit, depending upon whether the operator has plugged in only one cord or whether she has plugged in a number of cords. Assuming that she has answered a number of calls, as has been explained briefly in the first part of this specification, i. e., assuming that she has inserted the plugs of two or more cord circuitsinto calling line jacks, it is obvious that only one such waiting cord circuit must be connected to the head set 0 which is common to all cord circuits. The cord plugged in first, will complete the circuit including relay 30,

which has been traced above. No other, similar, circuits are connected at this time to the common conductor 45. Relay 30 operates therefore, and produces the following effect: It operates the armatures 31 and 36 and connects thereby the head set 0 to the talking conductors 25 and 26 of the cord circuit; at its armature 32, relay 30 shunts out resistance 33', thereby preventing subsequently plugged cord circuits to connect to the head set by energizing their relays 30; at armature 34, the common interrupter equipment I is connected to the cord circuit over the conductor 23, and at armature 35 relay 30 prepares a circuit for registering the extended call. This circuit will be completed when the operator inserts the calling plug P into the ack of the called line as'will be explained later. At the present time, the metering circuit cannot be completed because the metering relay37, which is connected to battery, is short circuited to battery by way of the supervisory lamp 76.

As has been explained above, the relay 30 has operated its armature 34 and connected thereby the interrupter equipment I to the cord circuit. An energizing circuit is now completed for relay 15 from ground, winding of relay 15, common conductor 23, arma ture 34 and its front contact, to battery over the supervisory lamp 22. Relay 15 energizes in this circuit: the supervisory lamp 22 however does not light in series with relay 15 due to the resistance of the latter. In operating, relay 15 closes a circuit for the pilot lamp 19 and for relay 16 at its armature 17. Relay 16 energizes and closes its armature 18, thereby connecting direct ground to the individual cord supervisory lamp 22. Lamp 22 lights. The ground connected at armature 18 of relay 16 short circuits relay 15. The latter deenergizes, thereby, interrupting the circuit of the common pilot lamp 19 and of relay 16. Relay 16 deenergizes now, removing the ground at armature 18, extinguishing the supervisory lamp 22, and permitting relay 15 to energize again as explained before. This mutual operation of relays 15 and 16 continues, resulting in a flashing indication for the operator. Relays 15 and 16 are slow-acting in order to produce a distinct operation.

The operators head set 0 is now connected to the talking strands of the cord circuit'and the conversational circuit is established. The

operator receives her information from the waiting calling party, and she takes the callthe calling party in the usual manner and disconnects the answering plug P from the line jack J.

However the called line B is assumed to be idle, and the operator inserts the calling plug P into the line jack J. The insertion of the plug produces the following circuit:

battery, winding of relay 40, conductor 54,

sleeve of plug P and sleeve of jack J, and

I equipment.

winding of cut-0E relay 84 of the called line to ground. The cut-off relay 84 and the relay 40 of the cord circuit operate. The cutoff relay removes the line relay 83 from the line conductors R and T in the usual manner. The relay 40, uponoperating, closes the following circuits: at armature 41 the ringback-tone circuit to the calling line is prepared; at armature 42 the circuit of relay 80 is interrupted; at armature 43 a circuit is prepared for the energization of the ringing relay and at armature 44 a circuit is established for the operation of the meter 47 and for lighting the supervisory lamp 76.

The metering circuit is closed over the following path: ground, front contact and armature 44, armature 85 and its front contact, conductor 24, winding of relay 37, to battery. Relay 37 energizes in this circuit and operates its armature 38 thereby closing an obvious circuit for themeter magnet 89. The meter magnet 39 01 crates the meter mecnanism 47 in a well known manner. Relay 37 is made slow-release to insure a full impulse for the meter magnet 39, since its circuit will be opened at armature 35 of relay 30 which deenergizes shortly after the operation of relay 40, its circuit having been opened at armature 42. However, relay 30 is also made slow to release, for the same reason, i. e., to insure against a faulty operation of the metering The head set of the operator will be disconnected from the cord circuit upon the deenergization of relay 30 at armatures 31 and 36. At armature 34, relay 3O disconnects the common interrupter equipment, thereby extinguishing the supervisory signal lamp 22 and the pilot lamp 19. Should the operator have connected another cord to another waiting line, the relay in this other cord, corresponding to relay 30, will now operate and complete the listening circuit and the flashing listening indication in this other cord, as was described in a previous paragraph.

c The operator selects now the proper frequency for ringing the called line. She depresses one of the ringing keys 9093, thereby also operating the starting key, corre sponding to the ringing key which she has depressed. The ringing key, as has been eX- plained elsewhere, remains in operated position while the starting key is only operated for an instant. The operation of the'starting key results in the following circuit: ground, one of the starting keys 6669, conductor 56, winding of the ringing relay 7 0, back contact and armature 51, and armature '43 and its front contact to battery. The ringing relay 7 O operates in this circuit and closes a locking circuit for itself which extends over its armature 73, armature 61 of relay'GO, conductor 58, front contact andarmature 2 1, and

front contact and armature 11 to ground. The rlngmg relay 70 is therefore locked up and made independent of the starting key. The ringing relay has the following functions: at its armatures 71 and 75, it connects the calling end of the cord circuit which is plugged into the called line jack, to the ringing equipment; at its armature 7 2 the generator G is connected to the upper talking conductor 25, of the cord circuit, by way of condenser 7 9 and armature 41 of relay 40; at its armature 7 4 the answering supervisory lamp 76 is extinguished. The operator has now completed her part in the extension of the call.

Ringing current is projected out to the called substation from superimposed battery of a ringing generator of the proper frequency by way of one of the conductors 6265, depending on which of the ringing keys has been depressed by the operator, conductor 55, ring cut-oil relay 60, front contact and armature 71, conductor 77, tip of plug P and tip of ack J, line conductor '1, bell of the called substation, line conductor T, ring of jack J and ring of plug P, conductor 78, armature and its front contact to ground. vVl ile the called subscriber is being rung, a ring-back-tone of a constant frequency, regardless of the frequency projecte'd out on the called line, is transmitted back to the calling line, from the generator G, front contact and armature 72, condenser 79, armature 41 and its front contact, talking conductor 25, condenser 8, talking conductor 6, and to the calling station over a circuit which has been traced previously.

It will be seen from the above that the operator, aftershe has once depressed the ringing key, is eliminated and has no possibility of entering the connection. The service rendered is therefore on the basis of secret service.

It shall be assumed next that the waiting subscriber abandons the call before the called subscriber replies. He restores the receiver to the switch-hook, thereby interrupting the line circuit and denergizing the supervisory relay 20 of the cord C. The supervisory relay 20, upon deenergizing, interrupts the locking circuit of the ringing relay 70, and this relay deenergizes and disconnects ringing current at its armatures 7 5 and 71; at its armature 72 relay 7 O disconnects the ring-backtone; at its armature 78 it interrupts its own locking circuit; and at armature 74 it closes the circuit for lighting the supervisory lamp 76. This lamp. lights now from battery, over armature 74 and its back contact, armature 52 and its back contact, and armature 44 and its front contact to ground. Relay 40, it will be remembered, is the sleeve relay of the calling end of the cord, and, since the cord is connected to the called line jack by means of plug P, the sleeve relay 40 is energized. Armature 21 of relay 20, being now in the position shown in the drawing, and armature 11 of the sleeve relay 10 being in operated position, since the sleeve relay 10 is energized in series with the cut-off relay 2 of the calling line, a circuit is completed for'lighting the calling supervisory lamp 22, from ground, .armature 11 and its front contact, armature 21 and its back contact, supervisory lamp 22, to battery. The operator observes that both supervisory lamps 22 and 26 are lighted and will remove the plugs P and P from the jacks J and J, thereby restoring all circuits to normal and conditioning the cord circuit forthe next call.

In case the calling subscriber desires to recall the operator he does so by again removing the receiver from the switch-hook. He will thereby cause the operation of the supervisory relay 20. The only consequence of this operation, at this time, is that the supervisory lamp 22 is extinguished- An energization of the relay 30 is not possible because of relay 40 being still energized over the sleeve conductor of plug P at the jack J. By jiggling his switch-hook, the calling party is able to recall the operator by flashing the supervisory lamp 22.

It will be assumed now that the calling subscriber has abandoned the call and that the operator has removed the plug P from the jack J, but has not removed the plug P from jack J. In this case, only relay 10 and relay 2 remain operated, relay 20 having deenergized when the receiver was replaced and relays 4:0 and deenergizing when plug P was removed from jack J. Since relay 14 is energized, lamp 22 will be glowing steadily. Now if the calling subscriber should initiate another call before plug P has been removed from jack J, supervisory relay 20 will energize with the removal of the receiver from the switch-hook, extinguishing lamp 22 at its armature 21. If the operator is extending no other calls, relay 30 will energize to start interrupter I which in turn will flash light 22 as has previously been explained. The operators head set will be connected to the calling line by the energization of relay 30 and the extension of the call from this point on will be as previously explained. If, however, the operator is busy in extending other calls, the relay 30 will not energize until she has completed those calls as has" already been explained. When the calls have been extended, the relay 30 will then operate and the process will be as described before.

It shall be assumed now that the calling subscriber does not abandon the call, but awaits the reply of the called party. When the called subscriber removes his receiver in order to answer the call, a circuit is instantaneously closed for the operation of the ring cut-ofi relay 60. This circuit extends over the same path as the ringing circuit. Since the called party is assumed to have removed his receiver from the switch-hook, it will; be apparent that the alternating current circuit leading over the bells and a condenser at the substation in the usual manner,is interrupted, and a direct current circuit is closed over the hook and through the transmitter and receiver of the substation. Since superimposed of the ringing relay 70. 'The latter, indeenergizing, disconnects ringing current in the usual manner, and also disconnects the ringback-tone generator G. Its other functions have been explained previously.

The line circuit being closed nowat the called substation, the back bridge relay 50 will operate from ground, upper winding of relay 50, front contact and armature 41, back contact and armature 71, talking strand 77, tip of the plug P and jack J, line conductor R, transmitter of the called substation, line conductor T, ring of jack J and plug P, talking strand 78, armature and its back contact, and lower winding of relay 50 to battery. The voice current transmission is accomplished by way of the talking conductors 25, 26, and the condensers 8 and 9; and the transmitter feed for the calling and called station is accomplished over the supervisory relay 20 and the back bridge relay 50 in the usual manner. Relay 50, upon operating, disconnects, at armature 57, the initial circuit for relay 70 to prevent reenergization of relay 70 should the operator accidentally actuate one of the ringing keys at this stage of the operation. At its armature 52 the back bridge relay 50 opens the circuit for the calling supervisory lamp 76.

Upon the termination of a call the calling and called subscribers replace their receivers. The operator receives disconnect supervision as follows: When the calling party replaces his receiver the supervisory relay 20 deenergizes and closes a circuit for the supervisory lamp 22, extending from ground, armature 11 and its front contact, armature2l and its back contact, and lamp 22 to battery. The

supervisory lamp 22 lights as a disconnect signal for the calling party. lVhen the called party replaces his receiver the back bridge relay 5O deenergizes and closes the circuit for the supervisory lamp 7 6 from ground, front contact and armature 44, back contact and armature 52, back contact and armature 74, and lamp 76 to battery. The operator, noticing that both lamps light, withdraws the plugs P and P from the line jacks J and J, thereby restoring all apparatus to normal position. The cordcircuit is now ready for the next call. 7

It will be seen from the abovedescriptio n that the cord circuit contemplated by the present invention presents many advantages over the art as known, and is useful and efficient in its application. There is only shown one form of carrying out the invention, but it Will be readily seen that the invention can receive a variety of expressions and that other forms of carrying out the invention Will suggest themselves to those skilled in the art. Itwill therefore be understood that it isnot desired to limit the invention to the precise form shown in the drawing. That is considered new and desired to have protected by Letters Patent Will be pointed out in the appended claims:

What is claimed is: g

1. In a telephone system, a calling station terminating at a plurality of operators positions, a called station, cord circuits in each of said positions for extending calls from said calling station to said called station, a super visory lamp signal in each of said cords, means operable upon connecting a cord circuit to said calling station, for conditioning the cord circuit to be used in extending a call, means for preventing more than one of said cord circuits to be so conditioned if a plurality of cords are connected to said calling station, and means for intermittently operating the lamp signal of the cord that has been conditioned.

2. In a telephone system, a calling station terminating at an operators position, a called station, a cord circuit in said position for extending calls from said calling station to said called station, a supervisory lamp in said cord, means operable upon connecting said cord to said calling station, for conditioning the same to be used in extending a call, and means for intermittently operating said supervisory lamp to signal the operator after the cord circuit has been conditioned.

3. In a telephone system, a calling station terminating at a plurality of operators positions, a called station, a cord circuit in each of said positions for extending a call from said calling station to said called station, a supervisory lamp signal in each of said cord circuits, an operators telephone set at each of said positions, means in each of said cords operable upon connecting a cord to said calling station, for automatically connecting the associated operators telephone set to that cord, means for preventing more than one cord from completing a connection With an operators set if a plurality of cords are connected to said calling station, and means for intermittently operating the supervisory lamp of the cord circuit to which the associated head set is connected to signal the operator.

4. In a telephone system, calling stations terminating at an operators position, called stations, a plurality of cord circuits for eX- tending connections from said calling stations to said called stations, a supervisory lamp in each of said cord circuits, an operators telephone set common to said cords, means for connecting said cords to said calling stations, means in. each of said cords for automatically connecting said cords to said *operators telephone set, means forpreventing more than one of said last mentioned means from operating if a plurality of cords are connected to calling'stations, and means for intermittently operating the associated supervisory lamp when a cord establishes connection With said operators telephone set.

5. In a telephone system, a calling station terminating at an operators position, acalled station, a cord circuit for extending calls from said calling station to said called station, means for connecting said cord circuit to said calling station, a supervisory lamp signal in said circuit, means operative automatically upon said cord circuit being connected to said calling station, for operating said signal intermittently as a listening-in indication for the operator, and means for operating said signal steadily as a disconnect supervision for the operator upon termination of a call.

6. In a telephone system, a calling station terminating at an operators position, a called line, a cord circuit for extending calls from said calling station to said called stations, means for connecting said cord'tosaid calling station, a supervisory lamp signal in said cord circuit, means operative automatically upon said cord circuit being connected to said calling station for flashing said signal as a listeningin indication for the operator, means, operative upon the termination of a call, for operating said signal steadily as a disconnect supervision for the operator, and means operative upon the subscriber operating the switch-hook for again flashing said lamp as a re-call signal for the operator.

7. In a telephone system, an operators position having an operators circuit and a calling line terminating thereat, a cord circuit at said position for effecting connection between said line and said operator s circuit, visual means in said cord circuit rendered operable to indicate When such connecton has been eliected.

8. In a telephone system, an operatorsposition and a cord circuit thereat, an operators telephone set, a signal, means for auto matically connecting said telephone set with said cord circuit, and means for intermittently operating said signal to indicatesuch connection.

9. In a telephone system, an operators position and a cord circuit thereat, an opera tors telephone set, a signal, means for automatically connecting and disconnecting said set from said cord circuit, means for intermittently operatin said signal to indicate the connection, and means for stopping said intermittent operation to indicate the disconnection of said telephone set.

10. In a telephone system, an operators position and a plurality of cord circuits thereat, an operators-telephone set common to said cord circuits, a plurality of signals, means for automatically connecting said set with any one of said cord circuits, and means for intermittently operating one of said signals to indicate to which cord circuit said telephone set is connected.

11. In a telephone system, the combination of a calling and a called line an operators position and a link circuit thereat provided with answering and calling terminals, for effecting connections with said lines, means in said link circuit rendered operable when connection is effected between the calling line and answering terminal to visually indicate such connection, and means in said link circuit rendered operable when connection is eifected between the calling-terminal and called line to visually indicate such connection and to render said first means inoperable.

12. In a telephone exchange system, the combination of a calling and a called line, an operators link circuit provided with answering and calling terminals for effecting connections with said lines, signals for said link circuit, means rendered operable for operating one signal when connection is efifected between the answering-terminal and the calling line, means rendered operable when connection is efiected between the calling terminal and called line for operating another of said signals and to render the first said means inoperable, and means controlled by the calling line to again operate the first mentioned signal.

18. In a telephone system, a cord circuit for connecting a calling and a called line, a ringing key in said cord circuit for transmitting signalling current over the called line, and means responsive to the answering of the called subscriber for rendering said key ineffective.

14. In a telephone system, a cord circuit for connecting a calling and a called line, a ringing key in said cord circuit, a relay controlled by the called subscriber, and means controlled by said relay for completing a talking circuit through said cord and for rendering said key ineffective.

15. In a telephone system, a cord circuit for extending a connection to a called line, a ringing key for signalling on the called line, and means for preventing the transmission of signalling current over the called line by means of said key after the receiver has been removed from the hook at the called station.

In witness whereof, I hereunto subscribe my name this 18th day of August, A. D.

AUGUST W. STEINKE. 

